However, Chang'e 4 didn't touch down just anywhere: China parked the car-sized lander and its rover on the moon's far side— an enigmatic region that, until now, humans have explored from only above.

China's feat was celebrated around the world by space-exploration enthusiasts and even top-level NASA officials. After all, it could help unlock ancient secrets of the moon's violent formation, scan a crystal-clear night sky for radio objects billions of light-years from Earth, and even help locate deposits of water ice.

"America's space program has always set the example for the world. China's moon landing is a scientific achievement no doubt," Mark Kelly, a retired NASA astronaut, tweeted on Friday. But he added the mission is "also a reminder that we need to get back to policy over politics" or "the world might leave us behind" — with "we" being the United States of America.

Kelly is an astronaut who's as patriotic and informed as they come, and he calls developments in space as he sees them. He's also not alone in believing China may soon blow past the rest of the world in space exploration.

"This is more than just a landing," Alan Duffy, an astronomer at the Royal Institution of Australia, told the Washington Post after the landing.

Here's what the Chang'e 4 mission is, why China landed it on the far side of the moon, and why it should be a wake-up call, though not a shocking one, to the US and the rest of the world.

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Early in the morning of December 8, 2018, a Chinese rocket launched with Chang'e 4: the first mission ever to touch the far side of the moon.

A Long March-3B rocket carrying the Chang'e 4 lunar probe takes off from the Xichang Satellite Launch Center in the Sichuan province of China on December 8, 2018.Reuters

Lunar satellites and NASA astronauts had photographed the far side, but until January 3, 2019, no spacecraft had ever landed there.

"Chang'e" is the name of a mythical lunar goddess, and "4" signifies the mission is one of several over the past decade. China's previous robotic moon landing, called Chang'e 3, put a rover called Yutu or "Jade Rabbit" on the surface in December 2013.

The Yutu rover rolls across the lunar surface in December 2013.
China National Space Administration/Chinese Academy of Sciences

Chang'e 4 and its rover were initially backup hardware for Chang'e 3, so China decided to use them for the riskier mission to the far side.

But first China had to solve a problem: The moon blocks radio waves. When Apollo 8 astronauts flew around the moon for the first time in 1968, for example, they briefly (and expectedly) lost contact with Earth.

The famous "Earthrise" photo taken by Apollo 8 astronauts during their trip around the moon on December 24, 1968.NASA

China solved the problem by launching a satellite called Queqiao or "magpie bridge" (another mythological reference) in May 2018. It "sees" the moon's far side and can relay data signals to and from Earth.

An illustration of China's Queqiao relay satellite near the moon.
CNSA/CAS

After weeks of traveling through space, Chang'e 4 safely landed on the lunar far side and rolled out its Yutu 2 rover.

China was not very forthcoming with details about the mission's status, but lunar scientists at NASA helped pinpoint the Chang'e 4 landing site. One researcher used images distributed through state media to locate it.

The coordinates placed the landing zone inside a 111-mile-wide impact site called the Von Kármán Crater.

The crater is part of the South Pole-Aitken Basin: a 1,550-mile-wide scar made by a collision about 3.9 billion years ago. The event may have splattered deep-down geologic layers of the moon onto its surface.

A map showing the landing site for Chang'e 4.
Shayanne Gal/Business Insider

The Yutu 2 rover, which is designed to last three months, is recording images while it rolls across the far side. It also has ground-penetrating radar, a rock-analyzing spectroscope, and a device to study lunar water ice.

Meanwhile, the car-sized lander is recording its surroundings with cameras and will conduct several other experiments.

When the 14-day-long lunar night arrives, the lander will scan the skies above for radio waves. It may have the clearest-ever radio-based view of deep space. (The moon will block noisy emissions from both the sun and Earth.)

A visualization of the Cosmic Microwave Background (CMB): the oldest light in our universe, imprinted on the sky when the 13.8-billion-year-old universe was just 380,000 years old. The swirls in the image are polarization, or changes in the orientation of the light waves.
ESA and the Planck Collaboration

Altogether, Chang'e 4 is a stunning achievement, especially since NASA has not soft-landed any mission on the moon's surface since December 1972. That last US mission was Apollo 17.

NASA is working with commercial companies to get experiments on the lunar surface, perhaps this year. It's also developing a gigantic rocket called Space Launch System to send astronauts to the moon in the late 2020s — but the project is lagging behind.

Patrick Shea inspects a 1.3% scale model of the NASA's Space Launch System in a wind tunnel.NASA/Ames/Dominic Hart

China is now working on a spaceship, called the New Generation Manned Spacecraft, that could fly four to six people into orbit at once. It's also developing a new space station.

The country's ultimate goal with its Chang'e program is to establish a crewed moon base. "Odds of the next voice transmission from the moon being in Mandarin are high," Joan Johnson-Freese, who studies the Chinese space program at the US Naval War College, told CNN in December.

China is hoping to land a crew in the early 2030s, if not sooner, and the stakes are high. In addition to slam-dunking US achievements in spaceflight, there may be hundreds of billions of tons of water ice at the moon's poles.

A map of "cold traps" inside shadowy lunar craters at the moon's south pole (left) and north pole (right). Blue dots show locations where water ice may be present on or near the surface.NASA

Lunar fuel would take a spaceship a lot farther into the solar system. That's because it takes many times less energy to leave the moon's surface compared with the energy required to depart Earth.

China is exploring how to sustain people on the moon with its Lunar Palace program on Earth. Some experimental runs locked several Chinese students inside a self-contained environment for hundreds of days to see if they could survive in it.

Inside a simulated space cabin, in which students live as a part of the Lunar Palace 365 Project at Beihang University in Beijing.
Damir Sagolj/Reuters

NASA does not have any comparable life-support experiment and has no plans to begin one. Meanwhile, China is starting to outpace the US in education of its people in the fields of science, technology, engineering, and mathematics (STEM).

About 200 kindergarten children take part in a mental-arithmetic contest in Huaibei, a city in east China's Anhui province.REUTERS/China Daily

For decades, China has awarded more college degrees in STEM than the US, and in recent years more than four times as many. Having an army of skilled researchers has made the Chang'e moon program possible.

China has become a powerhouse of scientific research and technology products.

While US investment and progress in energy falters, China is using its rapidly maturing and expanding brain trust to develop next-generation-fusion and nuclear-reactor technologies.

The Experimental Advanced Superconducting Tokamak fusion device, nicknamed "artificial sun," is tested at the Institute of Plasma Physics under the Chinese Academy of Sciences in Hefei.
Jianan Yu/Reuters

China has even roped high schoolers into developing artificial-intelligence technologies for its military.

So, while January's far-side moon landing might seem esoteric, it is a major example of China's success in boosting its scientific, technological, educational, and economic standing in the world — one that might, as Scott Kelly warned, soon leave the US behind.